To be sure, I'm not certain I even know what a VST is...
Probably the first place to start is to make sure you don't confuse VST with VSTi.
Oversimplifying, a VSTi is a virtual instrument, such as a string or brass library of sounds. It's normally some form of MIDI but there are exceptions. A VST is itself a program but it is written to interface seamlessly with a DAW or other music program, hence the term 'plugin'. VSTs are primarily for adjusting audio, not MIDI.